The present invention pertains to apparatus and methods used in handling semiconductor devices and the like.
Semiconductor Integrated Circuits (ICs) are typically fabricated in wafer form. After fabrication, the individual chips are scribed from the wafer and then undergo numerous processing and handling steps before they are tested and packaged. A tape and reel assembly is typically used to transport the scribed chips to the individual processing stations. The tape and reel assembly includes a tape with a plurality of cavities spaced at regular intervals. Once a chip has been placed inside a cavity, the cavity is sealed with an adhesive tape so the chip can be safely transported from station to station by the tape and. reel assembly. Special devices, known as device transfer machines, are used to transfer chips scribed from a wafer into the cavities of the tape and reel assembly.
FIG. 1A illustrates a diagrammatic side view of a device transfer machine 100. The device transfer machine 100 is responsible for transferring a semiconductor device, such as a flip chip die 102, from a stretched wafer 104 to a cavity 105. The cavity 105 is included in a tape 106 of a tape and reel 108. The transfer to the cavity 105 is complicated by the small size, delicacy and orientation of the die 102. An exemplary flip chip die may be about 35 mils square, which limits the applicable handling techniques. In addition, after sawing, the die 102 is oriented with its solder bumps 110 facing up, however, the die 102 is to be placed in the cavity 105 with the solder bumps 110 facing down.
The device transfer machine 100 performs the transfer from the stretched wafer 104 to the cavity 105 in five steps. The first step involves attaining the die 102 from the stretched wafer 104. Typically, the die 102 is picked up by a loader arm 112. The loader arm 112 may a robotic arm or another suitable pick and place mechanism. FIG. 1B illustrates a closer diagrammatic view of a head 114 of the loader arm 112. The head 114 includes a vacuum tube 116. To hold the die 102, the vacuum tube 116 applies a vacuum pressure on the surface 118 of the die 102 between the solder bumps 110. In addition, a vision apparatus 130 determines if the right die is being picked up.
To flip the die 102, a flipper 122 is used. The flipper 122 includes two platforms 126 and 128 on either end of a flipper arm 124. In the second step, the loader arm 114 places the die 102 onto the platform 126. In the third step, an actuator 132 rotates the flipper arm 124 to flip the die 102. In the fourth step, a placing mechanism 136 takes the die 102 from the platform 126 on the flipper 122 and moves it to the vicinity of the cavity 105.
In the fifth step, the die 102 is placed within the cavity 105 of the tape 106 by the placing mechanism 136. A second vision apparatus 138 is used to determine the correct position of the die 102 in the cavity 105. The die 102 and cavity 105 may then be indexed. Subsequently, a cover tape 140 is applied over cavity 105 to contain and protect the die 102 during shipping.
The device transfer machine 100 is problematic for a number of reasons. The handling rate of the flipper 122 is typically less than a thousand units per hour. This represents a significant bottleneck in the overall IC testing and packaging sequence. Attempts have been made to increase the rotational speed of the elongated mechanical arm. However, the increased speed creates excessive rotational torque, causing the chip to move or even fall off the platform.
In view of the foregoing, a device transfer machine with improved throughput would be desirable.
To achieve the foregoing, the invention provides to a rotary flipper including a wheel having a plurality of stations. A semiconductor device is placed within a first station in a first orientation. While the semiconductor device is held, the wheel portion of the rotary flipper rotates and the next station receives another semiconductor device. When the first station reaches an unloading position, the semiconductor device is released. At this point, the semiconductor device is in a second orientation. The wheel also includes an intermittent position between the loading and unloading position in which another semiconductor device may be loaded into another station on the wheel.
In another aspect, to facilitate continuous transfer to a tape and reel, the size of the wheel and the spatial arrangement of the stations on the circumference of the wheel are proportional to the spacing of the cavities on the tape and reel. Advantageously, this permits continuous and synchronous motion between the rotary flipper and the tape and reel. In another aspect, the number of stations on the wheel is maximized to restrict the motion of the wheel to small steps, thus eliminating high torque movements required for high speed movement over a larger distance.
In one aspect, a vacuum pressure is applied within the station to hold the semiconductor device. The vacuum pressure for a station may be independently controlled or automatically upon positioning of the wheel. In one embodiment, the vacuum pressure is not used and a shield is used to contain the semiconductor device in the station during movement.
In another embodiment, the invention relates to a semiconductor device transfer machine including a rotary flipper.